Fluorescent antibody technic used for identification and typing of Streptococcus pneumoniae

A fluorescent antibody technic (FAT) has been developed for identification and typing of Streptococcus pneumoniae. The technic was first compared with the Neufeld test (NT) using polyvalent antiserum and isolates identified as S. pneumoniae. Of 197 isolates, 191 (97%) were positive by both technic, and six strains (3%) were negative by both methods. Both tests were also used for determination of pneumococcal types agreed in 23 of 25 tests (92%) but the Neufeld test gave false results in 2 of 25 determinations (8%). The polyvalent antiserum was used to examine by FAT direct films obtained from various specimens and the results were compared with Gram stain and cultures. Of 198 direct films in which gram-positive cocci resembling pneumococci were found, 154 were positive by FAT and 130 were positive by culture. FAT appears to be more reliable than Gram stain or culture. During a four-year period, isolated strains of pneumococci were typed by FAT and the results compared. A slight change in the incidence of the pneumococcal types was observed. Although the Neufeld test is simpler, FAT is easier to read and is a more reliable method if identifying pneumococci, especially in body fluids where the number of microorganisms might be limited. Also, FAT is a more reliable procedure in typing strains.